This invention claims priority of the German application 200 19 106.3 filed Nov. 12, 2000 which is incorporated by reference herein.
The invention relates to a stand, capable of being balanced, having a parallelogram carrier that accommodates a load and comprises at least three support arms, of which two parallel support arms are supported with respect to a base, and having a measuring unit in the area of one of the support arms.
Stands with electronic balancing mechanisms have measuring units which measure an imbalance. Such measuring units are, for example, published in U.S. Pat. No. 5,528,417, in DE 4320443 A1 and DE 4334069 A1 and in WO 97/13997 from the applicant. The known measuring units frequently measure bending forces or travel resulting from bending in a braked stand. If appropriate, they use angle sensors, optical position sensors or bending sensors. A braked stand is understood to mean a stand of which at least one support arm is held by means of a brake so that it does not pivot with respect to the uprights. In practice, such brakes are as rule arranged between points fixed to the uprights and parallelogram carriers or between adjacent arms of a parallelogram carrier.
The invention is based on the object of providing a new generation of measuring units which can be implemented with particularly cost-effective, available sensors and can be mounted as simply as possible and/or integrated into stand components. This object is achieved by the following measures.
In the area of one of the parallel support arms of the parallelogram carrier, preferably on one of the two horizontal support arms, a compressive-force, shear force or bending sensor is arranged, which measures forces between a part of the support arm that is connected to the load and a braked part of the stand, and provides the measured values for the balancing control system.
In the process, the following criteria are satisfied, or use is made of the following laws:
a) The support arm is held in a brake-free manner. It follows from this that, if the load is balanced, it remains at the selected location. However, if the support arm is not balanced, then the load tends to drift away from the selected location.
b) Provided parallel to at least one of the supports or on a support belonging to the parallelogram carrier is a sensor which detects this drift.
c) The measured drift behavior controls the balancing.
As a variant of a different type, a sensor is alternatively incorporated directly in one of the supports of the parallelogram carrier, and measures the bending or shear forces occurring there. As a result of integrating a sensor into a weakened or interrupted point of a support arm in a parallelogram carrier, firstly a good integrated solution is found, which saves space. Secondly, however, the measurement is displaced to a location which is present in any stand with parallelogram carriers. The measuring unit itself can therefore be produced as a standard product, which can be used in any desired parallelogram carrier.
This applies equally to the first-named variant, in which the drift behaviour of the carrier is measured on its outside. A shear force sensor is particularly suitable for the application in the sense of the invention, being mounted at the interrupted or weakened point on the support arm, or between the support arm and a support. The use of a shear force sensor is advantageous in as much as it is produced in large numbers for other purposes and can therefore be used extremely cost-effectively.
However, the invention is not restricted to the use of a shear force sensor in a parallelogram carrier, but instead also includes the use of a shear force carrier for imbalance measurement in a stand quite generally. This is because the finding relating to the possible use of a shear force sensor for balance measurement can be advantageous even in other stand designs which manage without a parallelogram carrier, particularly since it leads to a considerable reduction in cost and saving in space in the measuring device.
The state in which the imbalance forces in a support arm of a parallelogram carrier can best be measured is that in which at least one link of the parallelogram carrier is braked or in which the aforementioned support is braked, but the support arm itself can drift slightly. In particular when the sensor, which then under certain circumstances operates as a bending sensor is arranged in the vicinity of the brake, the imbalance can be measured with good measurement accuracy in the braked state.
Furthermore, the use of a platform weighing cell has proven to be particularly cost-effective.
The invention can advantageously be used in a new stand corresponding to the commonly-owned and concurrently filed utility patent applications U.S. application Ser. No. 10/010101 (corresponding to German application DE 200 19 105), U.S. application Ser. No. 10/010103 (corresponding to German application DE 200 19 109), and U.S. application Ser. No. 10/007168 (corresponding to German application DE 200 19 107) filed on the same date, Nov. 8, 2001, by the applicant, which copending U.S. applications are hereby incorporated by reference into the present application.